Wireless networking is becoming increasingly common in offices, retail establishments and other networked facilities. A wireless local area network (WLAN) has obvious benefits over a typical wired LAN in that it offers client users mobility to move around from place to place within a coverage area or “cell,” without having to operate from a wired port in a fixed location. And by not relying on wired ports, a WLAN reduces the amount of wiring necessary in a networked area, resulting in reduced deployment cost and lower ongoing maintenance.
In a WLAN, a client device (such as a laptop computer or hand-held device) includes a radio component such as a wireless card having an antenna and suitable radio electronics circuitry for converting electronic signals back and forth into wireless radio frequency signals. The mobile client device communicates with the WLAN through a wireless Access Point (AP) that also includes an antenna system with a radio electronic package, and further includes a wired connection to the network, which can include one or more servers, and shared peripheral devices such as printers, etc.
At the present time, WLANs typically operate in either the 2.4 GHz or the 5 GHz wireless radio bands, in accordance with the IEEE 802.11 (a) and (g) wireless protocols. However, with the increase in wireless networking, there is an ongoing need to improve wireless throughput and increase the number of channels through which wireless clients may communicate with the APs. As a result, there is interest in utilizing the unlicensed UNII bands.
The UNII bands are specified by the Federal Communications Commission (FCC). These UNII bands are low-power bands adjacent to higher-power bands licensed for fixed wireless, commercial services, etc. The power requirements for UNII bands are kept low to as to avoid interference with adjacent licensed and military usage bands. In order to preserve the low-power requirements, the FCC rules for the UNII-1 band (5150 MHz-5250 MHz) require that radio devices operating in these bands have integral or captured antennas, rather than removable antenna devices joined to the radio with a connector. The antenna cannot be replaced with a higher-gain antenna that would violate the FCC power limitations. WLAN devices which operate in the UNII-1 band may not employ an antenna connector, prohibiting the user from selecting a specific antenna to meet an application requirement. This lack of flexibility, which is not encountered in equipment designed for UNII-2, 3 and the ISM bands, must be resolved in accordance with the UNII-1 standards.
It would also be desirable to provide omni-directional coverage as well as directional coverage patterns, so as to provide an end user with a variety of deployment options. Most users in the 2.4 GHz band currently deploy either a low-gain omni-directional antenna arrangement in a ceiling mount configuration, or, alternatively, a low gain patch antenna arrangement in a wall mount configuration. Therefore, there is a strong motivation to provide the same types of antenna patterns in an AP operating in the UNII bands. However, the omni-directional antenna may operate with a different gain than a directional antenna leading to different peak radiated emissions levels from the system. So an AP system which is capable of exceeding these emissions levels by virtue of its conducted power capability and its complement of antenna deployment alternatives must be able to adjust its conducted transmit power in order to maintain compliance with all FCC rules.